Question

Give the chemical formula for (a) carbonic acid, (b) sodium cyanide, (c) potassium hydrogen carbonate, (d) acetylene.

Short answer

(a) Carbonic acid: \(H_2CO_3\) (b) Sodium cyanide: \(NaCN\) (c) Potassium hydrogen carbonate: \(KHCO_3\) (d) Acetylene: \(C_2H_2\)

Step-by-step solution

Identify the Elements in the Compound

Carbonic acid consists of hydrogen, carbon, and oxygen. Their symbols are H, C, and O, respectively.

Determine the Combining Ratios

Carbonic acid has the following combining ratio: 2 hydrogen, 1 carbon, and 3 oxygen atoms. It can be represented as H₂CO₃. (b) Sodium Cyanide

Identify the Elements in the Compound

Sodium cyanide is made up of sodium and cyanide ions. The symbol for sodium is Na, while the cyanide ion has the formula CN⁻.

Determine the Combining Ratios

Sodium has a charge of +1, and cyanide has a charge of -1. Therefore, one sodium atom combines with one cyanide ion (CN⁻) to form NaCN. (c) Potassium Hydrogen Carbonate

Identify the Elements in the Compound

Potassium hydrogen carbonate is composed of potassium, hydrogen, carbon, and oxygen. Their symbols are K, H, C, and O, respectively.

Determine the Combining Ratios

Potassium hydrogen carbonate has the following combining ratio: 1 potassium, 1 hydrogen, 1 carbon, and 3 oxygen atoms. Its formula is KHCO₃. (d) Acetylene

Identify the Elements in the Compound

Acetylene consists of carbon and hydrogen. Their symbols are C and H, respectively.

Determine the Combining Ratios

Acetylene has the following combining ratio: 2 carbon and 2 hydrogen atoms. It can be represented as C₂H₂.

Key concepts

Compounds Identification

Identifying a compound involves figuring out which elements are a part of it. This is the first step in writing a chemical formula. For each compound, you need to look at its name and determine the elements contributing to it.

Chemical names often give clues about the elements they contain. For example, sodium cyanide contains sodium (Na) and cyanide (CN⁻), a group consisting of carbon and nitrogen. Understanding these elements lays the groundwork for constructing the correct chemical formula.

Being familiar with common names and their corresponding compounds can make this task easier. For instance:

• Carbonic acid contains hydrogen (H), carbon (C), and oxygen (O).
• Potassium hydrogen carbonate includes potassium (K), hydrogen (H), carbon (C), and oxygen (O).
• Acetylene, a simpler compound, includes only carbon (C) and hydrogen (H).

Once you've identified all the elements in the compound, you can move on to determining how these elements combine.

Element Symbols

Every chemical element has a unique symbol, typically derived from its English or Latin name. These symbols are the shorthand used in chemical formulas and are crucial for communication in chemistry. They are composed of one or two letters, with the first letter always capitalized and the second, if present, lowercase.

Understanding these symbols is key. For instance:

• H stands for hydrogen.
• C stands for carbon.
• O stands for oxygen.
• Na stands for sodium.
• K stands for potassium.

Recognizing these element symbols allows you to read and write chemical formulas accurately.

When you see a formula like H₂CO₃, you should be able to translate it as two hydrogen atoms, one carbon atom, and three oxygen atoms forming carbonic acid. Knowing element symbols is essential for identifying what a chemical formula represents.

Combining Ratios

Combining ratios are the numbers in a chemical formula that indicate how many atoms of each element make up a molecule of a compound. They are crucial for understanding how elements combine to form compounds.

These ratios are determined by the charges of the ions involved or the number of atoms that usually join to create a stable compound. Here are some examples:

• For carbonic acid (H₂CO₃), the ratio is 2:1:3, meaning two hydrogen atoms, one carbon atom, and three oxygen atoms combine.
• In sodium cyanide (NaCN), one sodium atom pairs with one cyanide ion (CN⁻), which consists of both carbon and nitrogen.
• Potassium hydrogen carbonate (KHCO₃) includes one atom each of potassium and carbon, one hydrogen atom, and three oxygen atoms.
• Acetylene (C₂H₂) has a simple ratio of 2:2, two carbon atoms to two hydrogen atoms.

These ratios are reflected in the subscripts in chemical formulas. They provide a simple way to visualize how elements interact at the molecular level, allowing for clear communication and comprehension in chemistry.